Lighting arrangements with LEDs are used for an ever-increasing number of lighting applications. In many cases, an optical element is arranged in front of an LED to alter the light emission, such as e.g. a lens, a reflector and/or a collimator to obtain an emitted light beam of desired properties. The properties of the emitted light may depend on the exact positioning of the optical element relative to the LED. An exact and stable positioning of the optical element relative to the LED is essential to maintain stable emission properties over a wide range of operating conditions. In case of providing a stable position by bringing the LEDs and the optical element in direct contact, there is a high risk of brittle failure of the LED material. Therefore, any contact between LEDs and optical elements are commonly prevented by certain holders providing a gap between optical element and LED emitting surface, where the structure should be stable in the range of a few micrometers.
Thermal changes, e.g. due to a change in ambient temperature or due to LED electrical operating power dissipated as heat, significantly influence such a holding structure provided to mount an optical element relative to an LED. In particular, if the structure supporting the LED and the optical element is comprised of different parts or different materials with a differing coefficient of thermal expansion (CTE), the structure may undergo distortions during negative or positive temperature increment that could lead to variations in the relative arrangement of the LED and the optical element.
It would be desirable to provide a lighting arrangement with improved thermal stability of the positioning of the optical element having relatively low temperature sensitivity over a wide range of operating condition even for significant mismatches of the coefficients of thermal expansion of the materials of the components of the lighting arrangement.